.
...for an adjustable wrench, these work pretty well on the majority of headsets:
Channellock 8SWCB Slim Jaw WIDEAZZ 8" Adjustable Wrench
Channellock 6WCB WIDEAZZ 6" Adjustable Wrench
Another thing that helps a lot is to have the fork ends clamped in some sort of holding device similar to this: